Switching mode inverters are used to convert direct current power into high voltage alternating current power which may be subsequently rectified and used for energizing electronic equipment such as computers, data processors, and the like. Such inverters operate on the principle of cyclically storing electrical energy from an appropriate source in an electromagnetic device, such as a transformer, and releasing the power from the electromagnetic device into the load.
Switching mode inverters, in general, appear in the prior art as push-pull circuits incorporating power switching transistors which are turned on alternately to provide a high voltage alternating current output with a rectangular waveform. The rectangular waveform is usually modified by reducing the total duty cycle below 100% so as to prevent cross-conduction during the switching of the transistors, and also to produce some means for regulating the output voltage by adjusting the duty cycle.
In order to operate the switching transistors in such an inverter at power levels approaching the inherent limitations of the transistors themselves, special attention is required to insure correct drive current occurs under all operating conditions. Non-optimized drive current will shorten the life of the switching transistors and promote rapid transistor failure.
Low power dissipation in the drive system of the invention is desirable so that inexpensive components may be used, and so that the components may be mounted closely adjacent to one another to minimize the effects of inductance without the need to consider increased heating effects.
Also, the technique of obtaining the power for the drive system from the switching transistors themselves reduces the need for auxiliary power, and inherently causes the drive current to be proportional to load current for regulation purposes.
In addition, transformer isolation, as is achieved in the system of the present invention, permits referencing the drive controls to other than the emitter of the transistor being driven, thereby simplifying control and auxiliary needs.